Miniaturized bio-analytical devices have become increasingly popular in the last few years because they have provided a robust, reproducible, bio-compatible, and reusable medium for rapid and parallel sorting, characterization, and sequencing of molecules. Some examples of these devices include using microfabricated obstacles, voids, channels and sieves as synthetic gel matrices for a non-traditional electrophoretic fractionation, fluorescent and diffractive identification. Further examples include the use of near-field and far-field fluorescence from hybridized molecular fluorophores as well as antibodies and other similar molecules.
Such techniques rely on optical means for identification, and hence usually require very specific chemical modifications that are appropriate for fluorescent measurement. Coupling fluorescent dyes to antibody molecules, which then serve as highly specific and versatile labeling reagents selectively binding to specific macromolecules, provides for a powerful technique of identification. The chemical labeling, however, restricts the technique to quite specific tasks that the fluorescent dyes and antibodies are available for and is time consuming. Other optical techniques, likewise, also require specific binding to be available and characterized for the optical method to avail. A general technique that could be used for a variety of applications and that provides a direct measurement of molecules is highly desired because it could provide a more general, unambiguous, accurate, inexpensive and rapid method. One such technique uses an ion-channel in a lipid bilayer membrane. It provides a direct measure of the charge across the opening between two reservoirs of macromolecules. The magnitude and duration of the measure is related to the magnitude of charges, the flow rates and the length of the macromolecule. Depending on the field and the magnitude of the charge passing through the ion-channel, the absolute magnitude of the change in current is in the pico ampere to femto ampere range and requires a very careful low noise measurement.
In a further prior art method, the membrane slit is replaced by a pore in an inorganic dielectric membrane on silicon. Changes in current in this method characterize the transport of molecules. Both these techniques, in principle, could provide a direct high speed detection of the sequence of bases in single molecules of DNA and RNA, but depend critically on measurement of ultra-small currents and ultra small pores.